Implantable pulse generators have been utilized to provide electrical stimulation to various organs, tissues, muscle, nerves or other features of a patient's body. One example of electrical stimulation provided to a patient is cardiac pacing. Cardiac pacing electrically stimulates the heart when the heart's natural pacemaker and/or conduction system fails to provide synchronized atrial and ventricular contractions at appropriate rates and intervals for a patient's needs. When a patient's heart is beating too slow, bradycardia pacing increases the rate at which the patient's heart contracts to provide relief from symptoms associated with bradycardia. Cardiac pacing may also provide electrical overdrive stimulation intended to suppress or convert tachyarrhythmias, again supplying relief from symptoms and preventing or terminating arrhythmias that could lead to sudden cardiac death or need to be treated with high voltage defibrillation or cardioversion shocks.
Pacemakers typically require at least two electrodes to deliver electrical stimulation therapy to the heart and to sense electrical activity of the heart. Traditionally, pacemaker systems are comprised of an implantable pulse generator (or pacemaker) coupled to one or more leads. The lead(s) include one or more electrodes on a distal portion of the lead that are implanted inside the heart such that at least one electrode touches the endocardium. In other examples, the one or more leads can be implanted on the epicardial surface of the heart.